Assays have been developed for the measurement of binding for an organic cation (N1-methylnicotinamide, NMN) and for organic anion (p- aminohippuric acid, PAH) to particulate material obtained from dog, rat, and rabbit kidney cortex tissue. The binding characteristics are those which one would expect a biologically important system would have. The research will be directed toward establishing whether or not the observed binding is a component of the transport processes for the organic ions. The experimental approach will be along two paths: one will be to correlate binding with known in vitro and in vivo physiological properties of transport. For example: a) correlation of specific binding with altered states, b) localization of binding sites with transport sites, c) correlation of competitors for finding with competitors and inhibitors of transport. The second experimental approach will be to complete the purification of the binding proteins in order to obtain chemically defined components. So that, perturbations of the transport system, produced enzymatically, chemically, or with specific antibodies, can be related to these proteins. In addition, this approach will supply information about the cell membrane systems.